Why did rice become a chinese staple food during the tang dynasty?
a. foods other than rice were available only to tang emperors.
b. confucian philosophy mandated eating only rice and no other foods.
c. drought made all types of crops other than rice nearly impossible to grow.
d. new types of rice and new growing techniques yielded bigger harvests.

d.new types of rice and new growing techniques yielded bigger harvests.

Explanation:

The Tang Dynasty, generally considered the golden age of Chinese culture, was founded by the Lǐ family, which took power during the Sui Dynasty's decline and collapse.

It was during the Tang Dynasty that the Silk Road was reopened, which allowed the increase in maritime trade in sails. The Tang managed to gain many new technologies, cultural practices, rare luxuries and foreign items. Cultural practices allowed rice cultivation to improve, agricultural waste and losses became smaller, new varieties of arable land were discovered, and increasingly technological agricultural practices allowed huge harvests. Which made rice increasingly popular in China.

the answer is a) high entry costs